A method and apparatus for filtering debris; and more particularly relates to a novel and improved method and apparatus for separating fish from debris and allowing water passage for all ranges of liquid flow.
Rotational drum screens for filtering water and separating debris are known in the prior art. Typical rotating drum screens require frequent maintenance and are difficult to clean as well as being costly. The drum filter typically includes a rotating drum positioned in a filter container. Water flows into and through the container, passing through the filtering screen of the drum. Debris typically lodges on the face of the drum screen filter, requiring a screen cleaning device to prevent complete obstruction of water flow. Currently, drums have been turned using one of three traditional methods; overshot, undershot and gear motor. The overshot drum relies upon the passage of water through the top 45% of the drum face. The lower 55% of the drum face is protected by a shroud that covers this portion of the drum. While this rotation is effective in providing a clean drum, the quantity of flow is severely limited due to the drum surface area that the water can flow through, and the requirement that the water level on the downstream side of the drum must be substantially lower than on the upstream side of the drum.
The undershot drum utilizes the full face of the drum for water to pass through. The rotation of this drum is accomplished with a paddle wheel on the inside of the drum and a gear train to drive the rotation of the drum member. As the water flows through the drum, the momentum and mass of the water flow drive the rotation of the paddle wheel. The drum rotation is in the opposite direction of the rotation of the paddle wheel. As is common with any mechanical gear driven device, maintenance may be difficult and costly. Where there is insufficient differential head across the drum, the drum will fail to rotate and typically become congested with debris. Low flows and low differential head severely impact the rotation of the drum and operation in a self-cleaning mode.
Where commercial power is available, or where solar panels and battery storage is provided, it is possible to drive a drum utilizing a gear motor, sprockets and a chain drive mechanism. The drums can be effectively rotated and the flow-through capacity can be high or low, although external electric motors, chains and sprockets provide a degree of liability and maintenance that often is not desirable.
An important application for rotational drum screens includes the filtration of water in rivers, lakes and streams whereby fish are retained in a designated area while debris is removed and filtered water is allowed to pass through the drum into an outlet. This is especially important to prevent endangered species of fish from passing through into agricultural diversions. The rotating drum is positioned perpendicular to the flow of water and rotation of the screen allows for filtration of the water while preventing fish from passing into an outlet.
Accordingly, there is a serious need for a self-cleaning rotating drum screen that also effectively acts as a fish deterrent while providing drum rotation irrespective of the flow rate of the water as well as providing a state-of-the-art filtration device that does not require an integrated electric motor to provide for rotation of the drum.